My laboratory has focused on gene transfer for the treatment of cancer. Cancer gene therapy includes a number of strategies including the replacement of defective tumor suppressor genes, expression of antisense molecules to inhibit dominant oncogenes, the transfer of immunostimulatory molecules and cytokines into tumors to increase their immunogenicity or enhance the effector cell response to tumor, the transfer of genes into tumors encoding enzymes that locally activate non-toxic drugs into cytotoxic agents, as well as antitumor vaccine approaches. Despite early optimism about "gene therapy," few meaningful responses have been reported in clinical trials. A major reason for this is the low in vivo efficiency of gene transfer achieved by most routine vectors and the inability to target sites of tumor that are remote form the point of vector administration. My laboratory has focused on expanding cancer gene therapy from what is essentially a local therapy to a systemic approach using "genetic vaccines" and oncolytic adenoviruses. A major effort in my laboratory has been the study of adenoviral vectors expressing non-transforming tumor-associated antigens (TAA) and antigen presenting dendritic cells modified using these vectors as antitumor vaccines. The Metabolism Branch has been involved in clinical trials studying the use of antitumor dendritic cell (DC) vaccines. In these studies, patients receive vaccinations with autologous dendritic cells that have been loaded ex vivo with synthetic peptide epitopes based on unique mutations found in oncogenes or tumor suppressor genes expressed in their cancer in hopes of stimulating specific cytolytic T cell responses against tumor. This strategy is predicated upon knowing the patient's MHC-type and the affinity of the peptide sequence for a specific MHC molecule. We explored an alternative approach involving gene transfer and expression of TAA genes in DCs. Vaccination with genetically altered DCs using recombinant adenoviral gene transfer has the potential advantages of: (1) expressing TAAs without the requirement for a detailed knowledge of a particular epitope or its binding affinity to an MHC molecule; (2) the ability to express larger antigenic sequences allows for the expression of a greater number of epitopes against which an immune response may be directed; (3) gene transfer and constitutive expression provides a continuous source of antigen to be loaded on to the MHC molecules overcoming the problem of low affinity epitopes that are rapidly lost from MHC molecules; (4) DCs naturally process the expressed TAA leading to more "effective" epitopes, and (5) the viral proteins associated with the vector may enhance DC maturation, activation, and recruitment of immune cells by providing additional signals to the immune system. We are studying this approach using the rodent neu and human K-ras oncogene antigens as targets. We generated recombinant adenoviral vectors encoding the neu oncogene extracellular and transmembrane domains (ECDtm), extracellular only (ECD), green fluorescent protein (GFP), and a control vector expressing no transgene (Ad.null). Using Ad.GFP, we found that murine bone marrow-derived DCs could be efficiently infected and the transgene highly expressed. Infection of immature DCs induced maturation and co-culture of nave splenocytes with transduced DCs stimulated greater proliferation in mixed lymphocyte culture compared to uninfected DCs or DCs infected with Ad.null. We examined antitumor vaccination using dendritic cells transduced with these vectors in a transgenic mouse model of neu induced breast cancer. BALB-neuT mice transgenic for an activated rat neu oncogene spontaneously develop breast cancers at 14 to 15 weeks of age and continue to develop tumors until 100% of the mice exhibit tumors by 25-weeks of age. We found that the longer cDNA, ECDtm, offered more protection from tumor compared to the shorter ECM.